The present invention relates to an apparatus and method for alarming decrease in tire air-pressure. More particularly, the present invention relates to an apparatus and method for alarming decrease in tire air-pressure capable of accurately correcting cornering and improving an accuracy for detecting reduction of tire pressure.
A conventional device (DWS system) for detecting decrease in tire air-pressure judges tire pressure reduction based on information from four ABS wheel speed sensors. The change of wheel speed is influenced by cornering as well as pressure reduction of the tires. According to the conventional DWS, all factors including the radius of cornering are calculated based on the information from the ABS sensors so as to decrease the influence of cornering and then a cornering correction is made. Even with this cornering correction, since the influences of the movement of load and slip generated during cornering are slightly change, the cornering correction cannot be completely made. According to the conventional DWS, however, the judgement values (DEL values) of the pressure reduction of tires calculated for about one minute are averaged and pressure reduction is judged based on the calculated average value. On an ordinary road, right and left curves exist almost in the same degree. For that reason, if a vehicle is running for about one minute, the influence of cornering is cancelled. Even if an error occurs to the cornering correction, therefore, there is few erroneous alarm caused by the influence of the cornering in the conventional DWS.
Nevertheless, if a vehicle runs on a circular track such as a test course, the vehicle runs only on a left curved passage or a right curved passage. Due to this, even if judgement values for one minute are averaged, the influence of cornering is not cancelled and erroneous alarm is sometimes given. This is because there is a rotational difference between inner wheels and outer wheels irrespective of normal internal pressure and this rotational difference cannot be distinguished from the rotational difference caused by pressure reduction.
In view of the above circumstances, the present invention has been made, and an object to provide an apparatus and method for alarming decrease in tire air-pressure capable of accurately making a cornering correction and improving an accuracy for detecting reduction of a tire pressure.
In accordance with the present invention, there is provided an apparatus for alarming decrease in tire air-pressure for alarming a decrease in internal pressure of tires attached to a four-wheeled vehicle using judgement values obtained based on rotational information obtained from the tires, comprising rotational information detecting means for detecting rotational information on each of the tires; memory means for storing the rotational information on each of the tires; arithmetic processing means for processing a judgement value from the rotational information on each of the tires; and judgement value correcting means for correcting the judgement value using a weight determined based on a rudder angle obtained by a rudder angle sensor attached to a steering wheel.
In accordance with the present invention, there is also provided a method for alarming decrease in tire air-pressure for alarming a decrease in internal pressure of tires attached to a four-wheeled vehicle using judgement values obtained based on rotational information obtained from the tires, comprising the steps of detecting the rotational information on each of the tires; storing the rotational information on each of the tires; processing a judgement value from the rotational information on each of the tires; and correcting the judgement value using a weight determined based on a rudder angle obtained from a rudder angle sensor attached to a steering wheel.